Polarization multiplexed receivers as well as optical hybrids have been described in detail in Kaneda, et al., “System and Method for Receiving Coherent, Polarization-Multiplexed Optical Signals,” Patent Application Publication No. US 2007/0297806 A1, Dec. 27, 2007, which is incorporated herein by reference in its entirety. Due to imperfections in manufacturing, temperature effects and other impairments of the optical hybrid in particular, the phase difference between the in-phase (I) and quadrature (Q) components may deviate from the ideal 90 degree separation. Such a deviation is referred to as a phase error.
In many systems the phase error results in a significant transmission penalty characterized by a higher bit error rate (BER) and, in optical systems, higher required optical signal to noise ratio (OSNR) for a given BER.
Methods for correcting phase error have been implemented in a digital signal processor (DSP). Known techniques include estimating the phase error and applying a correction factor derived from the phase error to one or both of the in-phase and quadrature components of the input signal. However, such techniques have been complicated.